Evaluation of the Flexural Response of CFRP-Strengthened Unbonded Posttensioned Members

This paper presents a synthesis of the results of a broad experimental and analytical research program undertaken for evaluating the flexural behavior of unbonded posttensioned prestressed concrete (PC) members when strengthened using external fiber-reinforced polymer (FRP) composites. In the experimental part of the investigation, the findings of which were reported earlier, 24 specimens were tested. The test variables included span-to-depth ratio, area of unbonded prestressing steel, area of FRP reinforcement, and profile of the prestressing tendons. An additional 12 companion bonded PC and reinforced concrete (RC) specimens having the same design parameters as the unbonded specimens were also tested for comparison. In the analytical part, numerical nonlinear analysis was carried out for analyzing the flexural behavior of FRP strengthened unbonded PC members and for regenerating the response of the specimens tested in the experimental part of the investigation. Also, a general design oriented model was developed, vis à vis the test results, for calculating the flexural capacity of FRP-strengthened posttensioned members with an internal or external unbonded tendon system. The procedure is consistent with the approach proposed in a standard-setting report for reinforced concrete or bonded prestressed concrete members, and is applicable for both simply supported and continuous members. A flow chart was developed for illustrating the use of the proposed design procedure.